This application claims the priority of Application No. 101 34 386.8, filed Jul. 14, 2001, in Germany, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a continuous wave radar system.
The continuous wave radar system has a transmitter circuit for generating radar transmitting signals, a transmit/receive antenna coupled to the transmitter circuit by way of a circulator, and a receiver circuit, which is coupled to the transmit/receive antenna by way of the circulator and which is intended to process radar echo signals of a target object. The radar echo signals are received at the transmit/receive antenna. The circulator serves to pass the transmitting signals, generated by the transmitter circuit, to the transmit/receive antenna and to divert the target object""s echo signals, received by the transmit/receive antenna, to the input of the receiver circuit. An RPC circuit is provided to suppress parts of the transmitting signals, diverted from the transmitter circuit and/or by means of reflection from the transmit/receive antenna directly into the receiver circuit in response to a control signal derived from the receiver circuit. The RPC circuit contains a reflection-modulator circuit connected into the signal path between the circulator and the transmit/receive antenna for the purpose of generating a correction signal compensating for the directly diverted parts of the transmitting signal.
In the past, the compensation or correction signal was obtained by coupling out at the transmitter output, by controlling the signal""s amplitude and phase via a quadrature modulator circuit and finally by feeding the signal into the signal path leading to the receiver circuit by way of a directional coupler. This past concept has the advantage of a substantial separation of the actual radar circuit and the RPC circuit as the additional component. However, it is expensive with respect to the number of components and their complexity, in particular, the quadrature modulator circuit.
A continuous wave radar system with a common transmit and receive antenna offers the possibility of generating the compensation and correction signal by means of a controlled reflection point in the antenna feed line and, thus, the possibility of forming a reflection modulator circuit. Such a concept has already been described by John D. Harmer and William S. O""Hare, xe2x80x9cSome Advances in CW Radar Techniques,xe2x80x9d Conference Proceedings of Nat. Conv. on Military Electronics, 1961, pp. 311-323. In this article, a three-dimensional waveguide module may be used in the form of a xe2x80x9cmagic T circuit,xe2x80x9d which can be produced only by waveguide technology, and is not suited for an integration of the circuit and where owing to the dimensions in the xe2x80x9cmagic T circuitxe2x80x9d the two stages for generating the in-phase signal and the quadrature signal on the connecting line have to be displaced in space at a distance of significantly more than xcex/8(xcex=wavelength on the line). Thus, a shift of the signals by 90xc2x0 may be realized for only a small frequency band.
An object of the invention is to provide a continuous wave radar system of the class described above that may be produced with components that are easy to integrate.
This problem is solved by means of a continuous wave radar system with features described herein.
Other advantageous developments of the continuous wave radar system of the invention are described herein.
The invention provides a continuous wave radar system, having a transmitter circuit for generating radar transmitting signals, a transmit/receive antenna, coupled by way of a circulator to the transmitter circuit, and a receiver circuit, coupled by way of the circulator to the transmit/receive antenna, for processing radar echo signals of a target object. These radar echo signals are received at the transmit/receive antenna. The circulator serves to pass the transmitting signals, generated by the transmitter circuit, to the transmit/receive antenna, and to divert the target object""s echo signals, which are received by the transmit/receive antenna, to the input of the receiver circuit. To suppress parts of the transmitting signals, diverted from the transmitter circuit and/or by means of reflection from the transmit/receive antenna directly into the receiver circuit, in response to a control signal, derived from the receiver circuit, there is an RPC circuit that contains a reflection modulator circuit, wired into the signal path between the circulator and the transmit/receive antenna, for the purpose of generating a correction signal, compensating for the directly diverted parts of the transmitting signal. The invention provides that the reflection modulator circuit contains a directional coupler arrangement for uncoupling a part of the signal, traversing the signal path between the circulator and the transmit/receive antenna, and a controllable line termination arrangement, attached to the directional coupler arrangement, for the purpose of setting the reflection and/or the absorption of the coupled out signal in the sense of generating the correction signal in response to the control signal, derived from the receiver circuit.
A significant advantage of this type of circuit is that the reflection modulator circuit may be produced in integrated circuit techniques by means of different line techniques. Another advantage of the present invention is that a quadrature (90xc2x0 shift of I and Q signals) is possible over a wide range of frequencies.
A preferred embodiment of the present invention provides that the directional coupler arrangement includes a first directional coupler and a first branch of the line, coupled by way of the first directional coupler to the signal path between the circulator and the transmit/receive antenna, for the purpose of coupling out an in-phase component from this signal path; and a second directional coupler and a second branch of the line, coupled by way of the second directional coupler to the signal path between the circulator and the transmit/receive antenna, for the purpose of coupling out a quadrature component from this signal path. At one end of the first branch of the line there is a first controllable line termination for setting the reflection and/or absorption of the coupled in-phase component, and at one end of the second branch of the line there is a second controllable line termination for setting the reflection and/or absorption of the coupled quadrature component. The coupled waves may be reflected with positive or negative phase or also totally absorbed by means of the controllable line terminations as a function of their control state. The reflected waves run by way of the directional coupler into the signal path between the circulator and the transmit/receive antenna, where they appear reduced in size by the coupling factor and run as the reflected waves backwards to the circulator, and from there to the receiver and may compensate for an undesired directly diverted signal.
Preferably, it is provided that a first absorber is located on the other end of the first branch of the line, and that a second absorber is located on the other end of the second branch of the line.
Another advantageous embodiment of the invention provides that the directional coupler arrangement includes a first directional coupler for dividing a first part of the signal path, which is connected to the circulator and is provided between the circulator and the transmit/receive antenna, into a first branch of the line and a second branch of the line. It further includes second and third directional couplers for coupling the first and second branches of the line to a third and fourth branch of the line, respectively. It also includes a fourth directional coupler for combining the third and fourth branches of the line to form a second part of the signal path, which is connected to the transmit/receive antenna and is provided between the circulator and the transmit/receive antenna. On one end of the branch of the line there are controllable line terminations for setting the reflection and/or absorption of in-phase and quadrature components of the signal coupled from the signal path. This embodiment exploits the property of directional couplers of 90xc2x0 phase shift of the coupled wave and the wave on the main line, a factor that can be used for the purpose of quadrature and extinguishing portions of the signal.
Preferably, one end of the first branch of the line is provided with a controllable line termination, and the other end of the first branch of the line is connected to the circulator.
Furthermore, it is advantageous if one end of the fourth branch of the line is provided with a controllable line termination, and the other end of the fourth branch of the line is connected to the transmit/receive antenna.
Preferably, a controllable line termination is provided on one end of the second and third branches of the line, and an absorber is provided on the other end of the second and third branch of the line, respectively.
According to another preferred embodiment, a line length difference of xcex/8 is provided between the second directional coupler and the third directional coupler in order to obtain a 90xc2x0 shift of the signals reflected in the second and third branch of the line.
It is preferable for the controllable line terminations, allocated in pairs to each other, to be provided on one end of the first and third branches on the line and on one end of the second and fourth branches of the line.
In all of the embodiments, the controllable line terminations can be formed by means of PIN diodes, by means of FET circuits or by means of varactor diodes.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.